A recent growing popularity of Internet of Things (IoT) has accelerated the development of such major wearable devices as watches and glasses that allow for Internet access. Even in the fields of medicine and sports, wearable devices for constantly monitoring the user's physical state are increasingly demanded, and such technological development is expected to be further encouraged.
One typical wearable device is attached to the human body of users to constantly monitor the state of physical conditions. The wearable device normally includes a bio-electrode for detecting an electric signal transmitted from a body, wires for sending the electric signal to a sensor, a semiconductor chip serving as a sensor, and a battery, as well as an adhesive pad to be attached to the skin. Patent Document 1 describes detailed structures of a bioelectrode, a wiring part surrounding the bioelectrode, and an adhesive pad. The wearable device disclosed in Patent Document 1 includes a bioelectrode, a silicone-based adhesive film disposed around the bioelectrode, a sensor device, and a meandering-shaped stretchable silver wiring part coated with a stretchable urethane film between the bioelectrode and the sensor device.
The urethane film has high stretch and strength, and excellent mechanical properties as a film coated on a stretchable wiring part. Unfortunately, the hydrolysis inherent in the urethane film lowers its stretch and strength, while the silicone film has no such hydrolysis, but the strength inherently remains low.
The use of silicone urethane polymers, whose main chain has both a urethane bond and a siloxane bond, has been examined. Advantageously, cured products of the silicone urethane polymer are characterized by higher strength than a single silicone component and lower hydrolysis than a single polyurethane component. Such cured products unfortunately fail to achieve the strength equivalent to a single polyurethane component and the water repellency equivalent to a single silicone component, and the strength and water repellency are in-betweens of those inherent in silicone and polyurethane components.
On the other hand, another type of material, including blended polyurethane and silicone components, has been examined in e.g., Patent Documents 2 and 3, each describing a material obtained by blending an unreactive silicone component and a crosslinking polyurethane component. Formation of a film from such a material allows silicone to come up to the cured film surface of polyurethane (bleedout) to improve the water repellency on the film surface. However, the non-crosslinking silicone causes itself to come off the film surface, thereby readily reducing the water repellency. Also, since a surfaceless state doesn't enable silicone to come up to the film surface, the film obtained by sandwiching its both sides between sheets for compression molding has low water repellency.
In addition, the use of diol materials for synthesizing polyurethane having siloxane on a side chain has been proposed. Patent Documents 4 and 5 each describe a diol compound for forming polyurethane having a silicone component on a side chain. The side-chain silicone group shown herein is a linear silicone in which siloxane is bonded to a diol compound at a terminal group.